Published international application WO 99/23944 discloses a method and an apparatus which assess electrocardiograms, with the aim of obtaining parameters which can be associated with the individual risk of a person, by assessing electrocardiograms in the area of extrasystoles.
In the time domain, for example, an ‘onset’ is ascertained for that purpose. That is the difference in the mean values of the last normal RR-intervals before the extrasystole and the first normal RR-intervals after the extrasystole.
Another parameter in the time domain is the ‘slope’, That is the greatest retardation in frequency within a sequence of a plurality of heartbeat intervals after an extrasystole over a predetermined number of successive RR-intervals. The gradient of the regression degrees describing the retardation in frequency is ascertained. In conjunction with the slope its correlation coefficient is determined, that is to say a measurement in respect of the regularity of the slope which is formed by numerical averaging of a plurality of successive slope values.
It is known from WO 99/23944 that, with a low onset, a shallow slope or a low correlation coefficient of the slope, the risk of dying as matters progress is significantly increased.